Area of Interest

Our group concentrates on the synthesis of novel polymeric materials. Among our areas
of interest are rigid rod polymers with unusual architecture, new polysaccharide derivatives,
and asphalt polymer composites. Working with other members of the Macromolecular Research
Group, we characterize all new materials and ascertain their potential applications.
This research entails organic synthesis, monomer polymerization, polymer modification,
graft copolymerization and preparation of polymer blends.

Our research on polysaccharides focuses on two areas: modification of polysaccharides
to produce water soluble rigid rod or aggregating systems and conversion of chitosan
to a soluble quaternary ammonium derivatives with biocidal properties. Techniques
have been developed to convert carboxymethyl derivatives of cellulose, starch, chitin
or chitosan into water-soluble aminoamide substrates suitable for further elaboration.
For example we have produced quaternary ammonium adducts that can be used as cosmetic
components and drug delivery adjuvants. The new cellulose derivatives enhance the
viscosity of a formulation and exhibit biostatic properties. Recently we have developed
a technique for elaborating cellulose with dendridic substutuents in a effort to enhance
the concentration of substituents, and increase the rigidity of cellulose backbone.
The dendrimer architecture has potential applications in catalysis and drug delivery.
We are also interested in preparing cellulose-peptide graft copolymers with potential
activity in calcium sequestration. These materials will duplicate the properties of
natural chitin composites.

There is an unfilled need for new antimicrobial agents suitable for use as preservatives
in personal care products as well as for new biocides to which bacterial strains have
not yet developed resistance. We have observed that chitosan is readly converted to
3-trimethylammonium-2-hydroxypropyl-N-chitosan (CHI-Q188), N-Carboxy-methyl chitosan
can be converted to a N',N'-dimethylammonium propyl carbamoyl-derivative and further
modified by quaternization to produce a series of chitosan aminoamide quats.

The antimicrobial activity of CHI-Q188 against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa was determined using the minimum inhibitory concentration (MIC) test. The derivative
exhibited biocidal activity at least an order of magnitude higher than previously
reported chitosan antimicrobial agents. Derivatives of Quat-188 exhibited more moderate
activity. The chitosan aminoamide quats also exhibited good antimicrobial activity.
Efforts to elucidate the mechanism for this activity continue.

We are incorporating thiohydroxamic esters (Barton esters, BE) onto polymer backbones
and using them to produce of graft copolymers efficiently. Asymmetric decomposition
of BE’s promoted by either heat or light allows selective graft initiation by the
bound acyloxy radical fragments. Efficient grafting of vinyl monomers from BE-modified
polystyrene and poly(arylene ether sulfone) has been demonstrated. Utilization of
BE’s as free radical sources allows for the formation of TEMPO unimers, which have
been shown to initiate controlled radical polymerization. Appending these unimers
to polymeric backbones allows for controlled radical graft copolymerization.

Cellulose derivatives can be converted to either the corresponding N-hydroxypyridine-2-thione
ester (Barton ester) or carbonate. Either of these substituents could be photolyzed
to produce graft copolymers of cellulose with styrene, acrylamide or N-isopropylacrylamide
(NIPAAM). The styrene grafts were attached to cellulose backbone with labile carbonate
linkages and terminated with thiopyridine groups generated by chain transfer to initiator.
The NIPAAM copolymers exhibit a lower critical solution temperature; thermally reversible
gels form upon cooling a solution to 32°C. Photolysis of the Barton carbonate in the
presence of styrene and excess TEMPO produced a macroinitiator for controlled radical
grafting of styrene to cellulose. The technique affords an opportunity to efficiently
produce cellulose grafts of controlled lengths and to evaluate the influence of graft
length on both the molecular properties and blending characteristics of the new materials.

Finally, we are exploring reinforcement of asphalt with modified polymeric wastes to
develop an outlet for recycled polymers. We have found that slight modifications of
polyolefins do improve the compatibility of the polymers with asphalt, as well as
the compatibility of the various asphalt phases. Dynamic mechanical techniques are
employed to predict the properties of asphalt polymer blends in asphalt cements. Efforts
are directed to enhancing the properties most critical in producing blends with long
term stability. Further work on this project, in conjunction with the Louisiana Transportation
Research Center, will include the preparation, characterization and recycling of polymer/asphalt
cements.